text:
ExpressJet IATA code before "merger" with Atlantic Southeast?
Before 2011, Atlantic Southeast had the IATA 2-letter code "EV". Then,

On November 22, 2011, both ExpressJet and Atlantic Southeast Airlines achieved a single operating certificate that allowed them to operate as one carrier, using Atlantic Southeast's former call sign "Acey". Effective December 31, 2011, all flights began operating under the name ExpressJet.[7] ExpressJet currently operates as United Airlines Express.

(so says Wikipedia.)
What IATA code(s) did ExpressJet, or airlines which became ExpressJet, use until that time?

By looking at the Wikipedia article history, one finds that on 8 November 2011 (before the merger), the IATA code for ExpressJet was XE, the ICAO code was BTA and callsign was JET LINK.

Oh... clever trick. Should have thought of that myself. Thank you. But - was this the only code?

This revision claimes RU, and this one changed it to XE.


text:
Are engines automatically stopped in an emergency landing?
This answer made me wonder if engines are stopped automatically after an emergency landing as soon as one of the exit doors are opened.

(...) if the engine is still running, you're about to run forward into the area where you're at risk of being sucked into the running engine.

I'm not sure how high the risk would be to be sucked in or being blasted away by the jet-blast, I guess a lot of the emergency landings are because of engine failure so they aren't running anymore.
Maybe as an added extra - how long does it take for an engine to spin down to a safe RPM (so that it won't suck in people or blast them away)?

See also my old question Is there any emergency situation in which jet engines would not be shut down before passenger evacuation of a transport aircraft?

Generally, whenever you find yourself asking "will planes automatically do X in situation Y?", then ask yourself what the consequences will be if there is a malfunction and the plane does X when it wasn't supposed to because the sensors detected situation Y (or the computers believed the sensors did) when in reality no such situation existed. There has been a fairly large number of accidents the cause of which trace back to some sort of sensor failure, including some pretty high-profile ones (frozen or otherwise blocked pitot tubes seem to be a classic, but are certainly not the only ones).

@MichaelKjörling well, at least for me, aviation was always top notch technology - and as cars are gaining more and more automatic features, I was thinking along the lines of "surely planes have this already". My car is doing things which I wouldn't do at times, but there is always the manual override (at least for the things I've encountered so far) - I guess it is an engineering question which one is worse. Pilots are highly trained personell, so maybe opting for less automatism is best here.

Building on @MichaelKjörling's comment, engineers would examine not only the consequences, but also the probabilities of each situation. All sensors have some failure rate. Maybe your exit door opening sensors fails once per 100,000 flights. That's not too bad. But if an emergency landing is only once in a million flights, then whenever you detect the door opening, it's actually 10x more likely to be a sensor failure than a real event. I made up these numbers but this is the kind of thinking that goes into design.

@Arsenal:  But "top notch" (admittedly a subjective definition) cars tend not to have those sorts of automatic features.  Those are either for the terminally lazy (e.g. automatic transmissions, or self-opening rear hatches on SUVs), or for gearheads (e.g. Tesla's Autopilot).

@DanielKiracofe yeah I'm well aware on risk assessments - I guess (because I'm not working in aviation) that pretty much anything safety related ends up being either SIL-3 or SIL-4 (the aviation equivalent to that), so you'd probably need to have two sensors or even three to make it work.

Two sensors isn't nearly enough. If one of those fails, you've now potentially got yourself a 50/50 vote, and can't decide. For redundancy, you generally need at least three of anything, preferably implemented differently. Now add to this that it's not just sensors that can fail, but also power and signal cabling, or software that processes the signals on either end, or computers that this software runs on, ... and that everything safety-related has to be certified to a very high standard, and you can probably see that proper redundancy for safety-critical items doesn't exactly come cheap.

@jamesqf: re: automatic transmission for the terminally lazy -- I drive in France where automatic transmission is not the norm (far from it) and I love automatic transmission. Why? because for me a car is a utility which I have to drive but otherwise has zero interest. The easier it is to drive, the better. It is obvious that the really terminally lazy people are those who use a graphical environment on their laptop, instead of a text terminal session, editing their files in vi. This is what I call lazy!

@Arsenal I'm sorry, I don't know how could I've missed that.

@Arsenal If a car shuts down by mistake due to malfunctioning sensors (as has happened), it gradually coasts to a stop and gives the driver plenty of time to pull over, or at least turn on their hazards. The same is not true when you're cruising as fast as a race car tens of thousands of feet up in the air with 400 passengers.

I guess a lot of the emergency landings are because of engine failure
  so they aren't running anymore.

That is not correct - there are many types of emergency landings: inoperative or stuck control surfaces, landing gear problems, bird strike, explosive decompression, etc. Engine failure is one of the failures people talk more about because it is easy to practice.
In an emergency, obviously some system is not working. Therefore there is no automatic mechanism to shut down the engines - the pilots may need them running in a scenario that is not accounted for by the engineers. The timing of that action is determined by the pilots. (Actually there is never a mechanism to auto shut down the engines - emergency or not. Even in the event of an engine fire, the pilots have the option to continue running the engine).
How long does it take for an engine to slow down its RPM? Around 20 seconds seems enough. I have no data to support this though.

For the time to slow down an engine, the  information may be available in the chronology of NTSB's incident reports for incident involving engine failure (I haven't search yet)

Even if the emergency landing is because of engine failure and all engines affected by the engine failure have fully shut down, it's not necessarily a given that all engines have failed.

Is the mechanism for keeping the engine running in a fire simply "don't pull the fire handle", or is there an override for the handle's fuel shut-off?

@Mark That sounds like the beginnings of a decent separate question, but I'm pretty sure that in airliners, pulling the fire handle is an irreversible action.

There have been incidents, like Continental flight 426 in 1975 (DEN, cause was a microburst) in which the engines continued to run after the crash. Fortunately from the NTSB report it seems like the running engines didn't prevent passenger egress.

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text:
Are there airport identifiers assigned to heliports?
FAA databases list multiple Official Facility Names with a given Associated City Name, for example:

CITY: Fort Lauderdale
  FACILITY NAMES: Fort Lauderdale/Hollywood International (FLL); BSO Public Safety Helistop; Port Everglades; Broward Health Medical Center; Fort Lauderdale Executive (FXE).

Only FLL and FXE are airports. The rest are heliports. Are there airport identifiers assigned to heliports?

Okay, so what are you asking?

There is no naming convention to distinguish them.

"Class B, C, D, E, G airports" - there's no such thing. Airports do not have classes, airspace does.

I edited your question to what I understand it to be. If I'm off track please edit it to clarify what you are asking.

Heliports are airports so they get assigned identifiers just as a fixed wing airport does

Generally, not all airports have an ICAO or IATA code. Helipads and small airports usually don't rank a code from either of them. IATA won't have any reason to assign a code unless there is some kind of passenger service out of them. ICAO won't have any reason unless there is some significant international service from there. There is more info on the criteria for ICAO codes on this question. Those helipads have FAA identifiers, though.

BSO Public Safety Helistop: FA10
Port Everglades: 2FD4
Broward Health Medical Center: 6FD8

FAA-only ID's have either three or four digits and always contain at least one number.
From the FAA's JO 7350.9K - Location Identifiers (p.1-2-3):

Two−letter, two−number identifiers are assigned to private−use landing facilities in the United
  States and its jurisdictions which do not meet the
  requirements for three−character assignments. They
  are keyed by the two−letter Post Office or
  supplemental abbreviation (listed below) of the state
  with which they are associated. The two−letter code
  appears in the first two, middle, or last two positions
  of the four−character code.

There are helipads that have IATA and ICOA codes, though. For example, West 30th Street Heliport (IATA: JRA, ICAO: KJRA, FAA: JRA) in New York.

"ICAO won't have any reason unless there is some significant international service from there." That might perhaps be the case in the USA, but I don't think it's the case globally. Wikipedia makes the (seemingly uncited) claim that "In small countries like Belgium or the Netherlands, almost all aerodromes have an ICAO code. For bigger countries like the UK or Germany this is not feasible," which seems plausible; certainly my local (Sweden) airport has an ICAO code, but insofar as I know zero non-GA or heavy traffic on the 1300 m runway.

@MichaelKjörling I'm sort of generalizing. I don't know the specific criteria for either ICAO or IATA to assign an ID. When I get a chance I'll do some poking around and see if I can find some specifics

@MichaelKjörling Added a link to a related (possibly duplicate) question about ICAO's criteria

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text:
What are the negative associations with Continuous Descent Approach?
According to this Wikipedia article:

Due to the negative association with the term CDA,[citation needed]
  new procedures introduced at LAX and other US airports are instead
  called optimized profile descent (OPD).

What are the negative associations with the term CDA?

There's a link on the Talk page for the article you quoted, which may help: "The FAA decided to rebrand CDA due to the safety and noise risks discovered oversease and in litigation so they changed the name of the procedure from “Continuous Descent Approach” to “Optimized Profile Descent” (OPD)."

Here there is a list of possible meanings of this abbreviation. Most of the interpretations are completely reputable and legitimate but maybe "Crash-Damaged Aircraft" is both negative and aviation-related.


text:
Would USAF ATC experience help in getting a civilian ATC job?
Can I join the US air force as an air traffic controller, and then use my ATC skills from my service to become a civilian ATCO?

Unless the military has greatly changed since I was in, the problem is going to be joining as an air traffic controller.

You can't guarantee the job you get when you join the armed forces no matter what a recruiter may say to you, it's all based on the "needs of the service". You could end up in logistics.

That’s not true at all.  You absolutely can come into a guaranteed job.  I did.

Yes, military air traffic controllers often transition to the civilian system after their military retirement. But if your end goal is the commercial world it might not be for you. The military want people fully committed to the job - committed enough to serve in a war zone where people would love to drop a bomb on your head. It is not something you can do for just a year or two and then move on, the minimum service commitment is, I think, 8 years. If you are motivated enough to accept all that then you can sign up after high school.
In the US the civilian ATC is run by the Federal Aviation Administration. Their requirements are on their website, and it looks like you'll need a degree or three years of suitable work experience. Once you meet those requirements you just wait for an advertisement and apply.

The FAA does have programs for veterans and some job openings are for candidates with experience only.


text:
Do jet aircraft have an emergency propeller?
I once heard, or misheard, this:

There is an emergency propeller that comes down in an emergency of jet-engine aircraft. It is behind the main landing gears.

Is this true or a story somebody made up?

It was used to great effect in the Gimli glider incident.

how cool is that ?!

I think you might have heard about the Ram Air Turbine, which is deployed in case of some aircraft in case of loss of main electrical power supply. From A320 Systems briefing:

In case of total loss of all main generators, the RAT is automatically extended and drives the emergency generator via a hydraulic motor.

The location of the ram air turbine varies with different aircraft and some of them (like the popular A320) have them near the landing gear. The following image is from @mins' excellent answer to another question.

Location of Ram Air Turbines in different aircraft, image from aviation.stackexchange.com

Bombardier BD700-1A11 Global 5000 (source)
Airbus A320 Flight test (source)
Bombardier CRJ700 (source)
US Navy T-45A (source)
Airbus A330 (source)
Boeing B747-8 (picture by Gregor Schläger, source)
Boeing B777, RAT extension switch (source)

Yeah, i saw the picture 2 before. Thanks!

The picture of the Lufthansa(?) technician really needs to be a caption competition.

I like the idea of it being an emergency propeller to fly the plane with.

How is this device automatically deployed in the loss of main system power?  Is it held back by some solenoid which lets go to deploy it when power is lost?  What happens when the plane is parked in a hangar?

@Wossname I'm guessing here, but batteries are one option. It's a lot easier to bring along batteries to run systems for a brief period and then augment the RAT, than to bring along batteries to run systems for however long is required to land the plane in case of an all-out power failure.

@Wossname You're right that the system is held back by a solenoid that deploys when the power is lost (or commanded by the pilot). Though they can be deployed manually when parked on hangar (automatic deployment is prevented when airspeed is less than a value), it is not recommended. You can see the linked question for further details.

@aeroalias: Wossname is asking why the system doesn't deploy automatically and unwantedly, when your plane is in the hangar powered down. Presumably the system is mechanically "armed" on take off then disarmed after landing before you disengage the electrical system.

@DavidRicherby: That is definitely a safety vest with a Lufthansa logo.

@mins Don't tell me, tell Wossname!

@Wossname: There are conditions for the RAT to be deployed, see Is there a maximum airspeed to deploy a ram air turbine? (there is a minimum airspeed and the logic on Airbus aircraft is this one).

@mins, +1 for the info.  I like the drawing style for that logic diagram, It's very clearly laid out (as it needs to be in a safety critical system!).  Good stuff.

@DavidRicherby: Caption for the photo: "What do you mean it flies?  Like, in the air?  I might be the new guy but I'm not falling for that one!"

@aCVn: Especially since aircraft already have emergency batteries (for that matter, some aircraft only have batteries, and no RAT).

There is a rotor, but not to provide thrust.
The rotor spins in the air stream to generate electrical energy, which is used to power avionics and hydraulic pumps so that the crew can continue to navigate and communicate.

In fact, it increases drag and speeds (slightly) the descent of the crippled aircraft, while supplying essential electrical energy...

I know this is pedantic, but a propeller is used to propel things. This would be a turbine.

The DC-10 had an under-belly propeller, driven by air during flight, as a backup power source in case of total failure of the plane's hydraulic system(s). The upgrade was shown on a Discovery Channel episode of "Mayday: Air Disaster."


text:
How does the Aerobridge dock with an aircraft?
What mechanism is employed by the Aerobridges to dock with the aircraft. I am not looking at how the plane docks but how the aerobridge manages to attach itself over the door of the aircraft? Is it some vaccum tech or what? From outside, one can only see the bellows/ flexible diaphragms.
What I am looking for is actually - how two non-conformal surfaces can be "joined" in order to create a sealed "lock" (assuming its closed from all other ends). This came to my mind and now I am trying to understand this as the situation is almost the same.

Well, the jet bridge does not actually join with the airplane. If you look at the place where the jetbridge and the airplane meet, there is a rubber bumper and some accordion cover (that just comes down on top of the doorway) which are the only things which touch the airplane. The two things never actually make a seal where they meet.

So that means if the wheels support is removed, that thing should just fall off, if I have understood correctly? It fooled me... I thought some kind of friction etc etc.. thing would be holding it up against...all wrong then...

Quite a few jet bridges also have an auto leveler sensor, a small rubber wheel, that touches the airplane. This keeps the bridge aligned while passengers offload and the aircraft gets "taller".

They're not attached to the aircraft in any kind of structural way (you can often see a small gap in fact). Same as a set of stairs pushed up to the aircraft door. It's just an object, anchored to the ground, that is directly next to the aircraft (and an auto leveler, as Ron notes). If the wheels were suddenly removed, then yes, the whole thing would collapse.

@ZachLipton and Ron Beyer ..Thanks a ton! I saw it all wrong then....my problem remains unsolved.. :/ Trying to get two such surfaces to attach and not just hold up against each other....Appreciate the prompt replies though :)

@fattypanda try velcro... lots of velcro

@JonStory  thanks for contributing. The thing is the weight in question (the project I am working on) is too much for even lots of velcro..plus its a tad inconvenient to get the velcro method done (couple pf constraints) I am currently pondering over vacuum/suction thing or Maybe this jet bridge docking with a support underneath. Have to do analysis and then figure out... never knew attaching two surfaces can be such a tedious task ;D

@fattypanda you can always try cold welding, although you'd have to really clean thai airplane and jetway surface (and probably create a slightly bigger vacuum around them).

@JustSid hmmm...seems fine but two problems mainly (btw this is my exact problem if it interests you :P - http://physics.stackexchange.com/questions/289049/ways-of-attaching-of-two-non-conformal-surfaces) 1. I wouldn't prefer the joint to be permanent (I guess cold welded joints are not preferred for really short span of time). 2. It might damage the surface. With reference to the link I gave, this should be clear. Would think about it though...thanks!

@fattypanda If you really want, you could have the jetway at a lower pressure than the outside and the canvas covering would be more flexible so the jetway just sucks onto the airplane.

@SMSvonderTann I get what you are saying....that would essentially be the "vacuum"/suction method..right? Most of the vertical climbing robots also use the same technique. Seems the best, I guess. Need to refine it.

Well jetways don't exactly 'dock' with an aircraft; there is no hard coupling between the tunnel and the airplane like say that found with a spacecraft docking.  Rather they are just maneuvered up against them with a soft canvas hood which can be actuated around the fuselage allowing protection from the weather for passengers and crew.
The jetway is maneuvered to and away from an aircraft via a small control panel near the hood of the jetway which controls an electrically driven wheeled drive supporting the terminus end of the jetway as well as screw jacks in the support pillars for elevation control.  This allows a user to translate the length of the tunnel or rotate it about its connecting point to the terminal.  The tunnel can do this by means of telescoping sections.  The terminus of the jetway can be swiveled to match the curvature of the fuselage and the tunnel makes contact with the jet at the base of the terminus, usually with a neoprene bumper to prevent damaging the fuselage.  The hood can then be lowered for weather protection.
The jetway will reverse this process after the main cabin door has been closed and secured and before pushback to prevent contact and damage with the aircraft during pushback.

@kevin got it sir. I meant to say that only, my bad :P naa. Any help offered in any way should be appreciated, I think that.  Its not for the reputation etc points :) :) thus accepted it. It cleared the doubt I had :)

To answer the actual question, unless you can draw a vacuum seal it's not really possible without throwing straps around the object being captured and pulling them taut to hold it in place.
And even then you'd need some kind of compressive material to actually cause some sort of seal between the objects.
But that of course is out of the realm of aviation and thus off topic for this site.

Actual docking systems always involve specially designed parts that hook up to each other and lock in place, plus a sealing mechanism (for example a rubber sleeve). Think the docking adapters on spacecraft, the in flight refueling systems on military aircraft.

Jet bridges do not involve parts that 'hook up'. This answer then does not answer the question (well, ignoring the vague, off topic bit)

@sanchises it answers the actual question, and if you read what I say you notice I nowhere say they "hook up" but that they should to make what he wants work. Learn to read and comprehend English.

Please refrain from being rude - just because I try to keep my comments short does not mean I do not mean well. This answer does not answer the on-topic aviation question "How does the Aerobridge dock...?" On the other hand, this answer does not provide a good answer to the alternative (in my opinion off-topic) question either, "how two non-conformal surfaces can be "joined"", since there are other methods than throwing straps around something (most obviously, clamping; but also magnetic, electrostatic, simply 'pushing' together, etc).

@jwenting  I can somehow understand what you are trying to say. But your last words regarding docking adapters has set me thinking, looking into it. As per the discussion I had with above people who answered, I understood that they just press against the surface of an aircraft and to prevent the plane from damage use a rubber tubing around the joining interface. Nothing "hooking up" tech involved. But throwing straps is something I definitely do not want to do. Suction seal is I am reading up on it. Other methods Sanchises mentioned - magnetic is out. Electrostatic adhesion, hmmm.need to think


text:
What is the speed of a standard airliner during the different phases of the flight?
I would like to know how does the speed of an airliner vary as a function of time.

Ballpark:

At the gate, 0 knots
Taxi, 5-30 knots (usually 10-20)
Takeoff, 150 knots (rough ballpark)
Climbout below 10,000', 250 knots
Climbout above 10,000', 270-320 knots
Climbout above 28,000', Mach .78 (ballpark)
Cruise, Mach .78 (groundspeed ~450 knots +/- wind)
Descent above 28,000', Mach .78
Descent 28k to 10k, 280 knots (up to 330 knots, if ATC requests)
Descent below 10k, 250 knots
Traffic pattern,200 knots
Final approach, 140 knots
Taxi in, 10-30 knots
At the gate, 0 knots

Edit: these are fairly typical 737 numbers; other aircraft will have differences. Regional jets will typically be slower; 747 and 777 will often be faster (especially for takeoff and cruise).

@jjack Mach 0.78 is within the usual range of cruise speeds for at least some common aircraft types, but something over Mach 0.8 could occur too. See the charts under Cost Index-Cruise Speed Relationship in http://ansperformance.eu/references/library/airbus-cost-index.pdf for example.

At the two 747-100/200 carriers I worked for, cruise was 0.86. Management at both companies advocated for 0.84, but both elected for cost reasons not to maintain the autothrottle systems that made that easy. Trying to maintain 0.84 manually was a seesaw operation that flight engineers might try for awhile. The easy thing to do, and which almost everyone did, was to select a power setting that put the airplane at 0.86, where it would stabilize (due we felt to a drag rise there) and not require continual adjustment.

@Terry: That worked well when fuel was 50 cents per gallon.


text:
Which items are allowed on passenger flights but not on cargo ones?
I've only ever sent items by air in suitcases accompanying me in passenger flights. But - I'm about to send some items on a cargo-only flight in a few days. I've been told:

Make sure that there are no dangerous goods in the shipment please (batteries, aerosols, perfume etc.)

while on passenger flights, you can definitely have batteries, aerosols and perfume in your hold luggage. You can even have that in the cabin under certain limitations.
So, my question is: What is the specification of which materials are forbidden for air transport in cargo flights as opposed to passenger flights? And is there a globally-accepted standard for this, or is it airline-by-airline?

You cannot have Li-on in your hold luggage.

It is generally frowned upon tho ship people on cargo flights though I'm not sure that it is forbidden.

@acpilot: When I wrote "items" I wasn't talking about people... :-)

Lithium-metal batteries are prohibited, full stop, in any form, on cargo flights, but are permitted inside personal electronic devices on passenger flights (for instance, the little coin cell in your laptop that lets it remember its CMOS settings, what day and time it is, that sort of stuff).

@Sean Lithium metal batteries contained in a device are fine in cargo aircraft. When shipped by themselves, not in a device the packaging requires pre-approval, but they can be shipped on cargo flights.

I don't know of anything that is prohibited on a cargo flight but not on a passenger flight. There are some things that are the other way around.
On a cargo flight you must declare any dangerous goods and usually pay a DG surcharge. Certain types of DG require seperation from other types. Some need to be segregated into a container that is accessible to the crew in an emergency or has a fire-suppression equipment.
Each country has its own laws as to what is acceptible and the proper documentation required. And each company will have their own set of rules. At my employer we use the slightly more stringent IATA guidelines. This ensures compliance with each country.
The passenger airlines are also required to follow these rules. Passenger luggage is contained in class C cargo holds which are required (at least in the US) to have a fire suppression system as well as a smoke detection system. In an all-cargo aircraft much of the plane is a class E hold, which must have smoke detection, but not a fire suppression system. Therefore certain types of DG have to be segregated into a class B or C area.
So, you can carry perfume in your luggage because the holds on a passenger plane are all class C, where there is fire suppression. But if you send a box of perfume in a cargo flight without declaring it, then it will most likely be loaded in a class E hold where it won't be compliant.

...How is perfume a dangerous good?  Also, why hold cargo holds to a looser standard than passenger holds?

@Sean Perfume almost always contain volatile solvents, therefore they are a flammable liquid. To install fire suppression equipment for the entire upper deck of a large cargo plane would involve a lot of piping and suppression chemical. So lots of cost and weight. Additionally it would have a limited effectiveness due to such a large space. Generally halon is used to snuff flames, but a huge area would require a very large amount of it. Since there aren't a large number of people susceptible to the effects of a fire they leave more leeway for the operators.

Did you mean "Class E" instead of "Class F" here, or has FedEx gone to Class F for all their main deck cargo (what with per-ULD fire containment/suppression and all)?

@UnrecognizedFallingObject I did mean class E. Thanks. I think the HazMat cans might be considered class F, but I'm not sure. They have their own fire suppression system separate from the rest of the cans. But they're always loaded in the front, right behind the net, so they might be class B.

@TomMcW -- ah.  it's still a class E then -- the designation applies to the hold as a whole.

Also -- fire suppression in Class E holds is accomplished through depressurization of the hold (although that's not always workable)

@UnrecognizedFallingObject The FAA AC says "Shutting off the ventilating airflow to or within the compartment controls a fire in a Class E compartment." That didn't work out so well for UPS flight 6. Self-sustaining fires is why they eliminated class D after the ValuJet crash. Li batteries have a similar problem.

@TomMcW -- yeah, that's what I was alluding to with the "that's not always workable" part.

@UnrecognizedFallingObject: Conceivably, couldn't you have separate ventilation systems for the flight deck and the cargo hold, install a blower just inside the hold's outflow valve, and, thus, be able to depressurise the cargo hold to below external ambient pressure by cutting off its bleed air supply and sucking out the air already in there?

@Sean -- negative differential pressure still won't help with something that brings its own oxygen to the party

@UnrecognizedFallingObject: It will if you keep sucking the newly-generated oxygen out fast enough.

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text:
Can an airline schedule two same-number flights to leave the same airport on the same day?
I've read: Why have different flights with the same flight number?
and I guess I understand this can make sense. But - is it allowed for a domestic US airline to schedule two flights with the same number, on the same day, with intersecting routes? Specifically, which have legs scheduled to fly out from the same airport on the same day?
This would be potentially quite confusing for passengers, even if the departure times are spaced many hours apart.
Motivation: I'm seeing what seem to be records of this occurring a few times in a USDT flight data table. Concrete example (edit: this is a significant example, but the question is about the general case) - some US airways flight legs from 2006:

uniquecarrier
flightdate
flightnum
origin
dest
crsdeptime
crsarrtime
tailnum
deptime
arrtime
cancelled

US
2006-01-25
634
LAS
PHL
645
1416
N632AU
642
1407
false

US
2006-01-25
634
LAS
PIT
2257
607
N808AW
2252
556
false

US
2006-01-26
634
LAS
PHL
645
1416
N621AU
650
1428
false

US
2006-01-26
634
LAS
PIT
2257
607
N833AW
2303
603
false

US
2006-01-27
634
LAS
PHL
645
1416
N633AU
643
1404
false

US
2006-01-27
634
LAS
PIT
2257
607
N832AW
2249
545
false

US
2006-01-28
634
LAS
PHL
645
1416
N629AU
645
1404
false

US
2006-01-28
634
LAS
PIT
2257
607
N806AW
2256
544
false

US
2006-01-29
634
LAS
PHL
645
1416
N602AU
640
1409
false

US
2006-01-29
634
LAS
PIT
2257
607
N827AW
2256
602
false

US
2006-01-30
634
LAS
PHL
645
1416
N632AU
641
1422
false

US
2006-01-30
634
LAS
PIT
2257
607
N801AW
2250
536
false

US
2006-01-31
634
LAS
PHL
645
1416
null
null
null
true

US
2006-02-01
634
LAS
PHL
645
1416
N628AU
652
1420
false

US
2006-02-01
634
LAS
PIT
2257
607
N810AW
2300
549
false

Related, possibly dupe: https://aviation.stackexchange.com/questions/44416/why-have-different-flights-with-the-same-flight-number

@RonBeyer: I linked to that question on the first line of my question...

It's quite possible you're seeing an error in the data. Can you post some here?

@CatchAsCatchCan: Yes, that's exactly what I'm wondering myself. Posted an example, or rather a few examples.

@CatchAsCatchCan: Would it help if I said these flights were by US airways?

Your bounty says, "help me figure out what's going on with this dataset" and then you edit the question to de-emphasize the data as merely the genesis of the question about the general case... it's your question, but this looks like you're shifting it back & forth  a bit.

@RalphJ: The dataset is about 10 GB of fight leg records.

Short Answer:
Flight 634 LAS-PHL at 0645 was most likely "US Air 634" on those dates, while flight 634 LAS-PIT at 2257 was most likely "America West 634" on those dates.  Even if both were to have flown with the ATC callsign "Cactus 634," that wouldn't be a problem for ATC since they were separated in time by several hours. (No more an issue than N12345 flying KABC to KABC more than once in a day.) But most likely, they flew with separate callsigns too, as explained below.
Why is this the likely answer?
The LAS-PHL flights in the OP were flown by aircraft whose registrations end in "AU" such as N628AU for example. The airfleets website shows that this aircraft was a US Air (later, US Airways) jet until it was re-registered in December 2006 (the dates on that site are DD-MM-YYYY format). Generalizing from that example, these jets were legacy (pre-merger) US Airways jets.
The LAS-PIT flights in the OP were flown by aircraft with registrations ending in "AW" such as N810AW. Airfleets shows that this was an America West jet until it became a US Airways jet in October 2006.  Again generalizing from this example, the "AW" jets were "American West" aircraft at the time of the OP's data.
So at the time, the one flight was being flown by jets in US Airway livery, and the other by jets in America West livery.  And to the passengers, they almost certainly were sold under the respective brands, so one could buy a ticket for "US Air flight 634" from LAS to PHL in the morning, or a ticket on "America West flight 634" from LAS to PIT in the evening. You'd have to use two separate websites to do so, but there would be no confusion.
Okay, so the remaining question:
Why do they both have the "US" (presumably meaning US Air) uniquecarrier ID in the table?
As described in this paper from Embry Riddle Aeronautical University,

America West Airlines acquired the bankrupt US Airways on September 27, 2005
to form the US Airways Group.

The two airlines became fully one in 2007, when a single operating certificate covered them both.  During the interim,

Both of the merged airlines retained their names and continued operating until September 25, 2007, when America West's FAA certificate was merged into US Airways.
(source)

This interim period is when the flights shown in the OP occurred.  At this point, the airlines were in the process of merging their operations, although their website weren't merged until May 2006.  Thus, in the January/February timeframe posted, the tickets for each would be sold separately.
The wikipedia article notes that the callsigns remained separate until 2008, as "US Air" and "Cactus"; after October 2008, the entire operation used "Cactus".
While it's hard to retrace each step along the way from two separate carriers to one unified carrier, it's clear that various steps are involved, so it seems probable that whatever data source gives the uniquecarrier identifier in the table, either switched over separate identifiers before the dates of these flights, or else it was retroactively changed over to make them all "US" even though at the time some would have been "AW".
In the general case...
So, is it possible, to have two flights with the same number at the same airport at the same day? Yes, although the data shown above probably doesn't indicate that LAS saw a "US Air 634" twice a day during the timeframe shown.  But as long as the first flight and the second don't overlap in time, there is no ATC constraint that prohibits is.  (Military aircraft do this all the time... Cool06 can fly from KDLF to KDLF on a training mission multiple times during the day -- Laughlin AFB in this case.) It's possible, but sufficiently unwise because of the potential to create confusion, that it probably happens for an airline somewhere between very rarely, and never.
As a matter of avoiding confusion, an airline would probably work to avoid scheduling their flight 123 more than once in a day:

"I'm here for my flight 123."
"Sorry, but YOUR flight 123 isn't for another 10 hours; this is the other flight 123 today."

But, if flight 123 is scheduled to depart at 2300 and one day it runs over an hour late, the next calendar day will have two "Flight 123" operations, and nothing will break.
All that to say, what the data in the OP most probably shows, is an artifact of how US Air operated during the transition from two airlines into one, and may not really be particularly indicative of anything more widespread, nor generalizable, than that.

From an air traffic control perspective, how the flights are referenced when marketing to passengers is not important. Instead the flight, or more correctly the aircraft, callsign is what matters.
Sometimes a flight will have an ATC callsign that is not the same as the flight number. For example Finnair operates a flight from Helsinki to Paris that is advertised as "Finnair Flight 1577" and likely displayed to customers as "AY1577" (AY being the IATA airline code for Finnair). But on ATC displays the flight shows as "FIN3EF" (FIN being the ICAO airline code for Finnair) and uses the callsign "Finnair Three-Echo-Foxtrot." This system seems to be used with more regularity among European airlines than American.
In the US, the callsign is almost always the flight number, but it doesn't have to be. One example I've noticed at my airport: There is a late-night arrival XYZ5163 from one airport, and an early-morning arrival XYZ5342 from the same airport. If the late-night flight is delayed long enough that they decide to run it the next morning instead, it will often have a callsign like XYZ534A, despite (I assume) having last night's flight number. ATC is also supposed to be alert for similar-sounding callsigns; if a controller notices confusing similar callsigns they're supposed to let management know (7110.65 2–4–15) and management will reach out to the airlines and see if there's a way to change one of the callsigns (7210.3 2–1–14).

So: as long as there is never more than one flight with the same callsign in the air at any one time, ATC doesn't care what the flight numbers are. That's as far as I know for the "faa-regulations" tag on your question. As for the marketing/passenger side, I think the other answers pretty well explain that USA and AWE were operated as distinct airlines until 2007. The Wikipedia article for AWE even says:

Beginning in January 2006, all America West flights were branded as US Airways, along with most signage at airports and other printed material, though many flights were described as "operated by America West." Apart from two heritage aircraft, the only remaining America West branding on aircraft were found on some seat covers and bulkheads. The merged airline used America West's "CACTUS" callsign and ICAO code "AWE", but retained the US Airways name.

So I think it's likely that whoever made your dataset assigned the "US" IATA code to both sides of the operation, or perhaps the operation itself used the "US" code for both, while ATC continued to see separate "AWE" and "USA" ICAO codes.

But what about the general case? You addressed the example. Is it never the case that the same flight number, of the same carrier (presented the same way to the passengers)

@einpoklum I can't speak well to that. Certainly what Ralph said is accurate, sometimes a flight scheduled to depart before midnight is delayed until after midnight—then you have two flights with the same number and destination that departed on the same calendar day. But I would guess that airlines try not to advertise them as departing on the same calendar day. I'm not actually certain how the flight number was described to customers in my "XYZ534A" example.

The crosses-midnight situation is not of interest to me, since I care about the scheduling (as you can tell from my example, my data is based on scheduled dates, not actual flown dates). And I also don't care about arrivals-cum-departures - just pairs of scheduled departures.

Yes it is possible to have flight with same number departing same airport at the same day when they have different flight number. By flight number I mean airline code combine with number. For example London Heathrow may have Imaginary Flight BA1, SQ1, CX1 and EK1 on the same day but they are different flight clearly mark by different airline code.
From your example, the pattern is clear. The flight to PHL operates by aircraft ending in AU while flight to PIT end with aircraft ending in AW. Brief google around reveals that aircraft ending with AU belongs to US Airline and AW belongs to American Airline. So it is just a case of different airline with the same number on the same route but differ by airline code. You need to pull airline name to see this pattern.

All these flights are listed under 'US Airways' in my dataset! Updating the table to better clarify this. Are you sure about the suffixes and airline association?

For a while, "US Air" included both "US Air East" - traditional US Airways, and " US Air West" - America West Airlines (which had actually bought US Air). This was long before the combined entity was bought by American.  One could hypothesize that one flight was sold as "US Air 123" while the other was sold as "America West 123". The convention at the time may have been that both operations got the same "unique carrier" ID (and perhaps flew as "Cactus123" - though widely separated in time), even though the public saw 2 separate brands.

A google search on N628AU shows that 757 in old-style US Air livery, and N810AW as being an America West bird until 2007. I suspect that the data in the OP is an artifact of how USAir operated during the transition from 2 airlines into 1, and may not be particularly interesting, nor indicative of more widespread nor generalizable trends, beyond that.

@RalphJ: So, the question remains - what about the general case?


text:
What are the ejection injury and fatality rates?
Most of us have probably heard about how ejecting from a military aircraft is dangerous in and of itself, and that ejection is not a get out of jail free card.
The most common dangers seem to be:

Lacerations during the ejection, by failing to clear the cockpit.
Concussions caused by collisions with the canopy or fuselage.
Insufficient altitude or speed to deploy a parachute before impacting terrain.
Other assorted hazards associated with parachuting down in an unprepared location.

There exist a number of openly-available reports on the topic, from several different countries and time periods that could serve as a starting point.
I have multiple closely-related questions, so I hope it will be self-evident why I chose not to split them up, but feel free to focus only on the first one:

What are the odds of surviving an ejection from a military aircraft? We can presuppose a fit crew member, but make no further assumptions about the particular case.
How likely is the crew member to sustain injuries?
Are there any significant trends in the data, e.g. introduction of 0-0 seats, survival procedures, sub- vs. supersonic ejection?

Its been 33 years, and this still brings back sad memories of Goose :(

https://www.smh.com.au/education/how-dangerous-is-it-to-eject-from-a-fighter-jet-20120730-239mp.html

I don't have any data to cite in answering your question, but there are a significant number of spinal injuries from ejection.  For that reason it is crucial to be in a proper position to reduce the risk.

Yes spinal compression problems are the main injury risk of an ejection. The newer seats are a bit more gentle though so it's supposed to be not so bad.

Note that focusing on American statistics means you miss out on the Russian Kamov Ka-50 "Black Shark", an attack helicopter with ejection seats.

Survival outcomes in low level ejections from high performance aircraft is a 2013 consolidation of ten separate studies of ejections from 1952-1997, focused on comparing low level to high level ejections. It doesn't state that these were military (though likely) and only considered those where altitude was known. From the abstract:

There were 562 low-level ejections identified. Out of this number, there were 274 fatalities, giving a low-level ejection survival rate of 51.2%. There were 2607 ejections that occurred above 500 ft (152 m), with a survival rate of 91.4%. There was a significant difference between ejection survival rates below and above 500 ft (152 m). Low-level ejections have a significantly increased risk of a fatal outcome (Odds Ratio 10.07).

So overall the odds of surviving an ejection are 84%.

Ouch!  90% chance of survival is much lower than I like; 50:50 sounds like really bad odds.  You clearly don't want to eject unless the alternative is worse.

Thanks for taking the time to write this up, after agonizing over the choice a bit I decided to give this answer the tick and Jpe61 the bounty, as a way of rewarding you both for the effort.

The abstract of the USAF take-off and landing ejections, 1973-85. gives an answer to two of your questions, leaving room for speculation as for the impact of 0-0 ejection seats (pun intended).
Direct quote, emphasis mine:

"...This review included only ejections clearly requiring a decision between ground egress and ejection. There were 15 aircraft with 25 crewmembers identified; 22 of them had ejected. Ejection systems performed as designed 91% of the time.
Three crewmembers were killed during ejection, yielding a survival rate of 86%. Four ejectees suffered spinal compression fractures from ejection force. Two of these also fractured other vertebrae during the parachute landing fall, for a major injury rate of 21%. In only 33% was ground egress probable. Survival and injury rates for ejection on the ground did not differ significantly from those above 500 ft (p less than 0.05). Ejection during take-off and landing phases is as safe as ejection above 500 ft. safer than other ejections below 500 ft, and does not result in excess injury rates. Ejection systems are sometimes damaged by impact or fire. In the emergencies considered, ejection offered greatly increased chances for survival over ground egress."

So, the statistics given by this study apply for ejection during take-off and landing phase and ejections above 500ft.
As for the trends after the introduction of 0-0 ejection seats, a non scientific conclusion could be drawn comparing statistics produced by the study above, and the one presented by @Pilothead in his answer. In the 1973-85 study the survival rate was 86%. In th 1952-1997 study the low level ejection survival rate was only 51.2% The higher survival rate of the 1973-85 study can partially be explained by the fact that some of the ejections in the 1952-1997 study were performed with a non 0-0 seat, since they were developed during the 1960's. The 1973-85 study does, however state that "Ejection during take-off ...[is]... safer than other ejections below 500 ft.", so a fully conclusive deduction cannot be made.
Unfortunately no studies on this subject are fully accessible to general public, so answers provided by @Pilothead and me are pretty much as good as it gets. :(

Thanks for taking the time to write this up, after agonizing over the choice a bit I decided to give this answer the bounty and accept Pilothead's, as a way of rewarding you both for the effort.


text:
What kind of aviation careers could I pursue?
I really want to be involved with airplanes and airports, but I'm not sure what the best career to go into is. I have thought a lot about air traffic control, piloting, and flight dispatching, but is there any other careers that I should think about?

Aviation is a large field,
You can work for an Airliners manufacturer, a Military plane manufacturer, Business Jet manufacturer, Small planes, ....
You have also opportunities in the safety field, like Flight Simulator manufacturer, Authorities, .....
The question is more about what are your competencies and what do you like to do. Because flying and air traffic control are really two different kind of jobs.

You don't have to have a precise plan to get started.
You didn't describe your age or education level, but you can probably find basic aviation classes at your local community college or flight school.  Start with some ground school, and lessons aimed at just a First Solo.   As you learn more about aviation, you'll see what appeals to you.
Some other related fields you might like are: A&P maintenance, Line Service, Aircraft Sales, Aviation Insurance, Aviation Law, Avionics.  (and probably many others)


text:
What kinds of jobs could a senior in high school get at a small local airport?
Is there anything a senior in high school could do for a small regional airport in Utah?

Sure! When I was a senior in high school I had a job as a line boy at a local FBO. We refueled aircraft, cleaned aircraft and moved them in and out of hangars. Not the most glamorous job but it was the beginning of the never ending learning process of aviation.

An FBO at my local airport (sorry OP, not in Utah)  advertised just such a position on FB earlier today. In addition to the usual benefits, they offer a discount on flight training. I wish I had thought of that in HS!


text:
When can a leg of a US domestic flight be flown after an earlier leg was cancelled?
Suppose a domestic US flight has legs A -> B, B -> C and C -> D. Now suppose, that on some day, leg A->B is flown, but then leg B -> C cannot be flown and gets cancelled (not delayed, cancelled). Will this necessary cause the cancellation of the C -> D leg...

If the flight was to have been flown by the same aircraft, and that aircraft is somehow able to be ready at C?
If the flight was to have been flown by the same aircraft, and that aircraft cannot be ready to fly at C?
If the flight was to have been flown by multiple aircraft?

Note: I'm asking about what happens in practice. That is, are flights always cancelled in these scenarios; sometimes cancelled; or never cancelled if C->D can still be flown

If the flight was to have been flown by different aircraft, it would be a different flight, not another leg of the same one, wouldn't it?

I don't think any kind of specific answer can be given. The dispatcher will try to get everybody to their destination with minimum loss and whatever they come up will happen. It might involve reassigning half of the airline's fleet and delaying completely unrelated flights.

@JanHudec: It's not absolutely necessary for all legs of a flight to be flown by the same aircraft, is it?

@JanHudec: "it might involve etc" - that means the cancellation is not necessary. Doesn't it?

Normally you only call multiple legs a single flight if all of them are not only flown by the same aircraft, but passengers who continue on the next leg don't need to disembark and embark again. Otherwise it is considered separate flights. It might still be one trip for you as a passenger, but that is a different matter.

No, it does not have to be cancelled. The airline still has the obligation to get everybody with valid tickets who checked in at the initial departure point to their final destinations and the dispatchers will do whatever they can and will be cheapest.

@JanHudec Some airlines will use the same flight number for multiple flights even if different aircraft are used and everyone has to change planes. That's still just the flight number and the number assigned to a flight segment isn't really relevant to whether it will be cancelled or not. That depends on all the circumstances related to the flight, which I agree makes this unanswerable.

@ZachLipton: I was under the impression that a flight is a sequence of flight legs, with the same flight number, forming a directed path from one airport to another. This, in accordance with the IATA definition of a leg, quoted here. Are you saying a flight may  actually consist of several disjoint paths? Also, it seems the example you linked to involves a domestic leg and an international leg; maybe that accounts for the anomaly.

This belongs on Travel.SE

I disagree.  I have numerous issues with this question and the OP's seeming non-cooperation with clarification, but it is relevant to the selected tags.  I agree that would also be appropriate on Travel SE to the extent that it affects the traveller's experience, but it is about operations and scheduling.

To the title question “when can a leg of a US domestic flight be flown after an earlier leg was cancelled?” the answer is:  When an aircraft and crew are available.
Dispatchers and operations managers deal with real world schedule changes regularly.   There are very real logistical issues that must be considered and dealt with such as weather, crew rest, flight hours and maintenance cycles on the aircraft, etc.  A change in one leg (such as a delay or cancellation) can have ripple effect on other parts of the schedule.  But, the OP offered three very specific scenarios, so let me address them:

"If the flight was to have been flown by the same aircraft, and that aircraft is somehow able to be ready at C?"  If the flight was to have been flown by the same aircraft, and that aircraft is somehow able to be ready at C, then there would be no reason to cancel.

This scenario makes no logical sense.  If leg B->C is NOT flown, then how might the same aircraft suddenly be available at location C?  Theoretically it could be disassembled and trucked there, but this is unrealistic.  If the OP meant that the airplane could fly there under a different flight number or callsign, perhaps empty of passengers as a non-revenue dead-head leg, then this needs to be stated clearly.

"If the flight was to have been flown by the same aircraft, and that aircraft cannot be ready to fly at C?"  If the flight was to have been flown by the same aircraft, and that aircraft cannot be ready to fly at C, then you would probably cancel the flight for lack of an aircraft.  (or move to scenario #3...)

This scenario makes sense, because if B->C is cancelled then the aircraft will not be available at location C.  However, the question is inane.  Of course you would cancel, you don't have an airplane to use!  If you don’t agree let me turn it around:  If no aircraft is available to fly leg C->D and you do NOT cancel that leg, then what might be your plan?  Please explain any options you consider valid.

"If the flight was to have been flown by multiple aircraft?"  If the flight was planned to have been flown by different aircraft, and that different aircraft was available, then there would be no reason to cancel.

This scenario makes sense, and is really the only scenario where the base question is valid.  I.e.  If an earlier leg is cancelled can another aircraft be substituted (or preplanned to use...) to complete the final leg?
The answer is yes.
Let me qualify my response by stating that I am not a trained or certified dispatcher.  I only work part time with a small part 135 carrier, but our bread and butter run is a three legged triangle we may fly several times a day.  In practice, we adjust flights whenever necessary to meet demand.
Consider this, you have been hired as a dispatcher, gate agent, regional operations manager, or some position where you have authority to impact the flight schedule, and your mission is to safely transport paying passengers in order to generate revenue for the company.  Today you find yourself in scenario #3:
You have an empty aircraft, fully fueled, a well-rested crew, a gate assigned, and a scheduled departure slot.  You also have a waiting area full of passengers anxious and ready to get on with their travel plans.  You have two options:

Option A:  Smile, key the mic and say “we are now ready to board flight ___ to D.”

Option B:  Smile, key the mic and say “Sorry folks, but because B->C was cancelled I cannot allow you to travel to D.  We are going to have to cancel this flight.”

What, in the name of all that is sensible, makes you think option B might be preferred?  And if you choose this option, how are you going to explain your rationale to 200 angry customers?
And good luck explaining to your VP of Operations why you just handed out thousands of dollar’s worth of compensatory travel vouchers, generated a bunch of negative customer satisfaction surveys that his bonus might be based on, and drove paying passengers over to the competition.
You had one job to do, and if you choose option B you failed!
Sure, in practice you may cancel, because there might be a later flight from C to somewhere else entirely that is higher priority, and a majority of your C->D passengers may have been on the earlier cancelled leg that you can pick back up tomorrow, (or even later that same day...) but this sort of additional consideration wasn’t asked in the simplified scenarios presented.

Do you know this to be the case in practice? That is, do you know of concrete examples of non-cancellations in cases 1 and 3?

In case 2, if C is a hub for that airline, there might be a spare plane and crew that could fly the final leg, so it may or may not be cancelled.

@einpoklum, perhaps I am missing some subtlety here, but in case # 1 & 3, why would you cancel a flight if an aircraft is available?  And for case # 2, how could you fly the leg if no aircraft is available?  Dispatchers deal with these sort of things regularly, and the goal is always to fly the flight schedule.  Perhaps if we understood the root of your confusion we could provide better answers.  Because right now your question reads like “if I need to go to the store can I take my car?  What if my car isn’t there?”

Because not all legs of the flight can be flown. Maybe the partial-legs need to be numbered differently (= different flight added at your discretion). Also, clarified that A->B is already flown by the time of the cancellation of B->C .

@einpoklum, I'm still not sure what your root question is.  Are you asking about renumbering the flight, or whether it is legal per FAA, and/or airline policy to load and dispatch an aircraft when an earlier leg has been cancelled?

@MichaelHall: I want to know if we actually see flights where A->B is flown, B->C isn't, and C->D is flown - as a leg of the same flight.

I get that.  Not helpful though...

@einpoklum, please see my major additions above and let me know if this helps clarify any confusion you still may have, or helps narrow down the specifics of your question...

So, you've basically answered my question, but - about the two options - there are actually three of them. The Option A notification read "we are now ready to board flight [original flight number] to D". Option C should read: Smile, key the mic and say "Attention passengers of flight [original flight number] to D: Your flight number has changed to [new flight number]. This is due to flight [original flight number] not being able to make it to this airport C. Boarding time remains unchanged. Please watch the monitors for notice of the boarding gate."

I appreciate the feedback, but changes to the flight number was not part of your original question. There are two options, cancel or don't. (changing the flight number is a sub-set of the "don't cancel" option)  Anyhow, I didn't intend my option descriptions to be a verbatim script, I simply wanted to liven up and illustrate those choices.


text:
Is it really required for a pilot to have good eye sight?
My basic knowledge says that it is not necessary for a pilot to have good eye sight,  he can use spectacles.
In an article I came to know that :
The United Kingdom Civil Aviation Authority state the following:
‘An applicant may be assessed as fit with hypermetropia not exceeding +5.0 dioptres, myopia not exceeding -6.0 dioptres, astigmatism not exceeding 2.0 dioptres, and anisometropia not exceeding 2.0 dioptres, provided that optimal correction has been considered and no significant pathology is demonstrated. Monocular visual acuities should be 6/6 or better.’
*Above eye problems are high level of eye defect.
• We should be worried on normal eye problem a serious problem to become a pilot ?

"An applicant may be assessed as": It might be interesting to know what the applicant is applying to.

I'm not sure I understand your question. Are you asking a) if any country requires pilots to have good eyesight even without glasses, or b) if good eyesight is important for pilots at all?

Asking about "any country" is too vague, and nearly impossible to answer since each country has its' own rules.  If you wish to limit it to the UK (which the article is discussing), or somewhere else, please specify so that it can be accurately answered.

@Lnafziger  there are many countries in the world do it is not possible for anyone to have info of all the country . In this section I think there are many pilots or related to that sector , so everyone will have different laws , condition .

@Pondlife you are right both

@user55439 That is exactly my point.  The question, as asked, is too broad to answer with a single answer, which is a requirement of this site.  In our terms, it is "too broad" to answer effectively.  I ask that you please narrow the scope to a particular locality so that it doesn't get closed.  See [ask] for more details.

@Lnafziger is it ok now ?

As worded this question is unclear. This may be a language barrier issue. Could you reword or say again your question to help us understand your meaning? help us

@JWalters thank you I got my answer . :)


text:
Where can I find a conceptual UML model of airline crewing activities?
I would like to know if anyone has created a UML model of the various elements of a typical crewing system. I have found online UML models for ticketing and reservation systems. However I would rather be interested in the crewing aspects. Here are the things I would like to model:

Flight Logs
Crew Activities
Pairings, legs
Etc...

I imagine airlines would keep that information proprietary, especially if it includes algorithms showing how they choose flight legs and balance resources like aircraft and crews since those directly effect profit.

Actually the crewing problem is well documented since it is a typical mathematical optimization problem.


text:
Charging system in a Lancair Columbia 350
The bus volts indication on my G1000 is pegged at 29.2 volts for both the left and right bus. I have a 24 volt system.  What might that mean?

Welcome to Av.SE!

the output voltage of a 24 volt system will be slightly less than 24V. the charge voltage will be significantly higher than 24 volts in order to push the charge into the battery. It therefore sounds like the battery charging circuit is stuck "on" where what it should be doing instead is continuously cycling on and off, on and off as the engine runs at cruise to keep the battery "topped off".
The charge system is regulated by either a mechanical relay or an electronic switch that senses system voltage and engages the charge function whenever the system voltage drops below a fixed threshold, indicating that the battery needs charging. If this system has failed, then either the charge system is on all the time (which is bad for the battery) or off all the time (which will let the battery run down and go flat).
Note that it is common for the charge circuit to run at 100% duty cycle right after starting the engine, because the charge state of the battery will be slightly depleted after a start. Then after several minutes of charging, the charge circuit will begin intermittently cutting out as the battery comes back to full charge until at equilibrium, the system voltage will jump momentarily up to 29 and then jump back to 24 for a while, then spike briefly at 29, then go back to 24, etc. indicating that the battery is once again fully charged.


text:
Is the airport a "No Man's Land" if I remain in the plane?
I have a daughter who lives in South Africa. I want to pick her up for Christmas Holidays but South African immigration wouldn't issue me a visa.
Can I land with a private jet and remain inside the plane while she boards, and then I take off? Will I be breaking the law if the jet arrives and I don't disembark from the jet?

This is probably a better fit for Law or Travel SE.  Or better yet, South Africa customs and immigration...

Not an answer to the question, hence writing it in a comment. You said you can remain inside the plane while she boards, which means she is able to go through the airport and board a plane all by herself without needing your help. Then, why do you need to go to South Africa to pick her up? She can just fly to your country all by herself. Also, if you are unable to go to South Africa because immigration wouldn't issue you a visa, I guess another option would be to send a person who you trust 100% to pick her up on behalf of you.

How is this different to a plane making a stopover on a trip to another place, with passengers who do not intend to disembark at the stopover, or at least not exit the airport?

There is no real "no man's land" at the airports. The host country still exerts all sovereig rights and all local laws apply in the transit zones.

The general case is that sovereign nations tend to want control over who enters their country, so the typical expectation is that an aircraft flying in from another country will first clear customs (at an airport with such a facility) at their first point of landing.  And that means that everybody disembarks.  Aircrew might be exempt from this requirement, but even that isn't a certainty. But if you aren't part of the crew, you probably would be expected to get off the airplane & clear customs.  And there may well be different rules for crew of an airliner vs the crew of a small jet.
There are exceptions to all of this, and I'm not familiar with particular rules that might apply to South Africa and wherever it is you'd be coming from.
There probably are places where one could get away with landing unannounced, picking up a passenger, and departing again, especially late at night, but "getting away with" something means that the rules are being broken, and the penalties if you get caught might be significant.  Not just for you, but for the owner of the aircraft -- if that gets impounded, that's an expensive lesson!  So unless it's your own jet, you may have a hard time finding an operator who is willing to put his aircraft at risk by agreeing to your idea.
Also, a private jet tends to fly high enough that flying IFR, and thus under ATC control, is the norm; doing that, it's harder to just go where you want to without anybody finding out.  And for an aircraft that flies into a country IFR, just cancelling IFR and going somewhere other than the filed destination under VFR is certainly going to arouse suspicion.  "You said you'd be landing at XYZ where you could clear customs, but now you're not going to XYZ any longer -- what's this guy up to???"
If you're serious about doing this, you really should talk to an operator who has experience flying into South Africa, and they can discuss the laws and practices specific to that country.  The general case would be, you probably can't do what you mentioned without breaking a law someplace, but general cases can have exceptions.

I don't think that the asker is intending to enter the country.  Remaining on the air side means that he doesn't leave international space.  This is no different to a transit passenger, who is able to leave the plane and return - only when passing through customs and immigration do you enter the host country.  When I've been a passenger on a long flight, there was never a requirement to get off the plane when stopping to refuel and for the partial-journey passengers to leave and join the flight.

@TobySpeight To "remain on the air side" is a thing with airline operations, but may not have any equivalent with small aircraft like private jets. Airline passengers are in a pretty tightly controlled environment, without any opportunity to wander in to an FBO for a cup of coffee, and then walk on out of the facility.  FBO's don't typically have the physical access controls that international terminals do, and thus the frequent requirement that everybody on the small jets clears customs. Again, as everybody has said, best to get info on specific arrangements in South Africa.

@RalphJ and that's a really interesting question and probably closest to what the OP is looking for. Is "airside transit" a thing in GA at all?

I'm no expert, but the passport-controlled areas of an airport appear to be separate from the rest of the nation in which they exist.  Passengers may disembark a plane, and if they do not have a valid reason for entering that country, may be asked to board the same or another plane and leave the country.
So, logically, you should be able to land in South Africa, exit the plane, meet your daughter and board the same or another plane at the same airport without requiring a visa.  It's little different to a plane needing to stop to refuel or deal with an onboard emergency and allowing the passengers to disembark to stretch their legs or move away from danger.  As long as you don't leave the airport or attempt to pass through border control at the airport, and as long as you're not a wanted fugitive in South Africa, you should be fine.
Just remember, IANAL, so check first, probably with a South African embassy.

They would not be able to meet their daughter inside the South Africa airport because she won't be able to enter the transit area. At best they can meet her on the plane to the next destination. And they likely would not be allowed to board an airline flight to SA if they don't have a visa. Nor can they book a flight from country A to country A which changes planes in SA. They would have to book a flight which makes a stop in SA on the way to a country that they are allowed to go to, and book their daughter on the same flight to that country.  From there they can both fly back to country A.

@StevePemberton, If the daughter has a passport - and a guardian if she's under-age - why would she not be able to enter the transit area?  If we're talking about a chartered flight, there shouldn't be a need for a SA visa if the stopover is for a pickup only.

Some countries have visa-free airside transit; others don't.  In this case, it's irrelevant unless the OP somehow manages to get a gate at the international section of the airport involved.

MontyWild - you are right I should have said they can meet at the gate for the next flight. By transit area I was thinking of the area that you enter into immediately after you disembark where you haven't technically entered the airport yet. Arriving passengers continue on to customs but at some hub airports there is another path for transiting passengers. I meant the daughter could not get into that "transition" area that arriving and transiting passengers are flowing through. But in the terminal you are right they can meet there.

MontyWild - Without a visa you must have an onward ticket booking to a third destination other than the one that you are coming from. This is also true for charter flights which are essentially the same as airline flights, they are just scheduled differently. But I realize now that you said "chartered flight" as in chartered airplane, i.e. a private plane as in the original question. Yes things are more flexible in that case. But then they won't be in the regular passenger terminal they will be in a different part of the airport and that is where the daughter will have to go to meet them.

@StevePemberton That would logically be the case, with the OP entering the SA airport with the express purpose of meeting his daughter in order to continue travel elsewhere.

I initially read your answer as suggesting an alternative solution to the OP's plan to fly privately, I thought you were suggested flying commercially and meeting the daughter in the passenger terminal. My comments were addressing that idea. But if you were just using passenger terminals as an example, and were using that example as a reason why on a private flight arriving at an FBO or whatever they call it in South Africa, that they could step off the Gulfstream that they chartered, walk into the FBO terminal, meet their daughter, then walk her out to the Gulfstream, I see your point.


text:
Why didn't Air Force Ones have camouflage?
The US's Air force ones currently uses Boeing VC-25s. There are many other models and aircraft used before the Vc-25. However, what I find interesting is that all images of Air Force Ones I've found so far do not wear a camouflage. Almost all military aircraft today have some kind of camouflage, so I'm wondering why Air Force Ones don't have one. Given that Air Force Ones carry the president, it is quite perplexing why these aircraft do not conceal themselves from potential enemy interception. They do have antimissile systems though, so it appears to me that they are designed for close quarter encounters and defense. Thus, not prepared to engage in close-quarter encounters as a reason for not having a camouflage is out of the question. Why not try to not be seen in the first place, instead of being seen and defending? So, do Air Force Ones really don't have camouflage, or is it just because my images are incorrect and incomplete? Also, if they really don't wear camouflage, are there any reasons for this? I'll appreciate any help.

Military transports don't seem to go in for camouflage much, unless they are in a 'close support' role. Even combat aircraft don't go in for it much unless they too are in a ground-attack role.

@MikeB "Even combat aircraft no longer go in for it much..." It faded out with the emergence of non-visual detection and especially air- and surface- to-air missiles post WWII. But AF1's predecessors have been flying since the 30s, when camouflage was the norm for gun-range combat, and seemingly used more on transports too.  While the Boeing 314 was sometimes painted in camouflage, I can't see any evidence that Roosevelt's Dixie Clipper was

Frame challenge: By not being painted in a camouflage pattern a potential attacker/enemy won't be able to use the "We thought it was a normal military aircraft" excuse. It's like when Biden visited Ukraine, by informing the Russian command in case anything happened the "It was accidental collateral, we had no idea the President was there or we wouldn't have done anything" reasoning won't hold. (Not posting as an answer since it's just speculation on my side)

Normal camouflage colors make the aircraft hard to spot in jungles. How often does AF1 fly into jungles?

@Barmar Camouflage is not used in jungles only. Of course, they work in jungles as well.

@AircraftEnthusiast007 Yeah, but what I think of as camouflage colors is greenish. More generally, you need different camouflage depending on where you're going.

They are camouflaged.
They spend most of their time operating from major airports alongside other airliners, so painting them to look unlike an airliner would make them more obvious.
Facetious answer aside, a big part of VC-25s is to project power and be seen, and making the aircraft hard to see would both defeat the purpose and indicate that there was fear of an adversary.
There is also a practical question of what scheme to use. Gray is used for aircraft intended to be hard to spot in flight, but is not particularly great when parked. Green/brown colours are used for aircraft where dispersal on the ground amongst terrain may hinder attack, but hard to see terrain/foliage that would hide a VC-25.
Then we have stealth black, which is not very useful during the day, and other more exotic schemes like pink or dazzle.
For all of these they have a situation where they are effective, and poor to terrible in others. So either a lot of repainting would be required, or accepting that a lot of the time the choice will be wrong. People are quick to make fun of and mock poor camouflage choices, and being mocked is not really the aim with the VC-25.
So a colour scheme that looks impressive, reasonably simple to maintain and not requiring additional certification from Boeing would seem a sensible choice for the VC-25s.
As a practical matter, a VC-25 getting into a close-quarter encounter where visual deception matters has already lost, given they will always be massively bigger than anything approaching them with ill intent. If this style of combat is possible you either want to charter an existing airliner, so you can look exactly like an airliner to visual inspection, or be stealthy on all wavelengths and ditch the 747 airframe, which may become a thing for traveling heads of state as high-tech weapon systems proliferate more.

I don't agree that your first two paragraphs are facetious.

"a big part of VC-25s is to project power and be seen".  That's the only phrase needed in the answer.

To emphasize the impressive argument, https://www.airandspaceforces.com/weapons-platforms/c-37/ is for highest ranking generals, and while equipped with IR defense, still has similar colors. Israeli counterpart's Wing of Zion https://www.haaretz.com/israel-news/2021-12-14/ty-article-static/will-it-ever-fly-inside-israels-controversial-300-million-air-force-one/0000017f-f0ea-d8a1-a5ff-f0ea52ba0000 have laser defense & similar colors. China lending a 747 to Kim Jong Un https://asiatimes.com/2018/06/inside-the-old-air-china-jet-that-carried-kim-to-meet-trump/ also counts as "impressive" factor.

Aside from the good answers about projecting power and radar, remember that it's very important to this country and its constitution that the commander-in-chief of the US military, the US President, is a civilian.  Even though the president and the Secretary of Defense are in charge of the military it would be horribly inappropriate for them to appear with the troops or anywhere in a military uniform, and it would be inappropriate for their clothing, airplane, limo, hot-air balloon, etc to symbolize membership in the military.
Note that the distinction is not so important for other countries.  Here is a picture of SecDef Lloyd Austin with his Chinese Counterpart. Both are retired generals, but Austin is wearing civilian clothing while Wei Fenghe is in military garb. In some places military juntas rule countries and govern in uniform to project power, but I hope that never happens in here in the US.

Personally I think this is the better answer. I'm also reminded of the Thunderbirds and the Blue Angels. Just because an aircraft is military doesn't mean it's meant for combat.

UK https://www.bbc.co.uk/news/articles/cv2gle48845o https://www.independent.co.uk/news/uk/politics/keir-starmer-military-photo-estonia-b2468597.html is not run by a Juntu. But wearing the uniform of the commander in chief seems to have gone out of fashion after Washington https://www.si.edu/object/george-washingtons-uniform%3Anmah_434863

@user84304 What other reason could there be? The other answers point out there is no tactical reason for a camo paint job, and certainly if a president wanted the military livery it could be done, so it seems obvious neither the president nor the military wants it, and this is why.

@PeteKirkham Mr Starmer certainly got some blowback for his costume. Also he was not PM at the time.

Because of its mission role, AF1 is immune to lawful interception. Camouflage would actually *endanger* the aircraft.
Others have covered the PR reasons and other defensive measures AF1 has at its disposal, so we can take those as read.  These are, however, subordinate to an important part of international law: Diplomatic Immunity.
Wherever they go, the President of the United States is a head of state. Everyone in their entourage, their immediate family members, and whatever infrastructure is necessary for the purpose of conveying them is therefore (at least de facto) part of a diplomatic mission.
From the Hague Convention:

An individual is considered a parlementaire who is authorized by one of the belligerents to enter into communication with the other, and who carries a white flag. He has a right to inviolability, as well as the trumpeter, bugler, or drummer, the flag-bearer, and the interpreter who may accompany him.

When traveling abroad, and especially in hostile airspace, the President is acting as a diplomat and is subject to all of the protections attaching thereto - including immunity from interception and an absolute right to not be fired upon.  AF1's livery is, therefore, the legal equivalent to the 'white flag of truce.'
Painting the aircraft in camouflage, or in anything other than a glaringly obvious "The President of the United States is on this plane" would actually raise the likelihood that an aircraft performing interception would mis-identify the aircraft as military in nature, and thus a legal target.  This would, in turn, endanger the President of the United States - the exact opposite effect camouflage is supposed to have.
This is why a 'white flag' is how you request a ceasefire for parlay - it's highly visible, very unusual on a battlefield, and cannot be mistaken for an attempt to conceal.  Trying to hide your 'white flag' so it can't be detected and fired upon by an enemy suggests that you're past the point where diplomacy is considered a realistic possibility... at which point the better protection for POTUS is to not be anywhere that could possibly be attacked like that. At which point, again, no camouflage needed (or, arguably, lack of being there is the supreme measure of avoiding detection - and therefore the very best camouflage).

Not a direct answer, but don't forget about the E-4B. The plane most people think of as "Air Force One", while quite capable, is more of a diplomatic transport. In the event of an all-out war, the president could use the E4-B, which has a less conspicuous paint scheme and stronger countermeasures. Of course, it still isn't "camouflaged", but it's also not a stealth plane. Anyone with basic radar or IR could find it easily anyway.

Note that the paint scheme is entirely functional. It is called "anti-flash white" and is supposed to reflect as much (infrared) light as possible to prevent the airplane overheating in case a nuclear bomb with its intense infrared thermal radiation explodes in its vicinity.

Great answer! Thanks for the information, especially for taking up the E-4B aircraft. I (and I guess even many of the people here) don't know of the E-4B, so many of us here, me included, learned a lot from your post! Again, thanks!

There are a few good answers here but I think there is a simpler one: there is no point in visual camouflage for the VC AF1 or any other aircraft POTUS may be in. There are multiple layers of protection involved including unseen escorts, no-fly zones along the flight path, constant monitoring both locally on AF1 and reconnaissance craft on land/air/sea, and, likely, a few tricks that are highly classified. As a side note, while it is possible that an attacker may attempt to visually identify a target, RADAR is far and away the bigger threat. Even the newest military aircraft are easy to spot from a significant distance visually. The advanced features on these craft make them invisible, or at least much (apparently) smaller, to RADAR and other electronic monitoring devices.

"Sky is big"
Or, to put another way, the VC-25s are camouflaged when necessary. When then-President George W. Bush visited the troops in Iraq on his, now famous but then top-secret, surprise Thanksgiving trip in 2003, the VC-25A filed a flight plan as a privately chartered Gulfstream V. That's generally enough "camouflage" for an airplane that looks like a civilian airliner.
And that was enough for pretty much the entire world to be convinced that President Bush was still sitting at the dinner table at his ranch. Even most of his own Secret Service detail working at the ranch hadn't noticed that he was gone until they saw it on the news, after he had already left Baghdad again.

Air Force One is the callsign of any USAF aircraft carrying US President. Air Force will eliminate any threat before allowing POTUS to fly in their aircraft. Hence camouflage is not necessary since there is no threat to protect from. You would not like to have POTUS shot down on your watch.

I'm not sure this tracks given the extensive countermeasures it has on board. https://simpleflying.com/air-force-one-defense-systems-guide/ . I'm sure they're not expecting to get shot at but they've clearly prepared to be

My understanding is those were in case of some nutcase with a shoulder fire missile hanging around near the airport.

While the first sentence is true, I don't think it's relevant in this context. There's a specific aircraft that is designed to be the President's normal transport, and that's what the question is asking about.


text:
How could a PA-28 be made to fly higher?
How would I have to modify the Piper PA-28 to fly at 25,000 feet (same as PA-34 and PA-46)? Could it fly higher?
Larger wings, other wingform, bigger motor something else? Do you have to change the whole construction of the plane?

Depends on how high you want to go. For the engine you'll probably need to switch to a turbocharged engine, which was available in some PA-28's like the Turbo Dakota and Turbo Arrow. Even then you only got about a 6000 foot increase over the non-turbo versions. You also have to realize that above FL180 you need to be operating IFR, so your aircraft must be IFR equipped and you be rated as a pilot.

I was just wondering, how far you could push a modified piper

That depends on the depth of your wallet. At some point it will be cheaper to just buy an aircraft that has a maximum ceiling around where you want to fly.

Related, possibly a dupe

@fooot what would you modify on the question? You're very welcome to make changes.

@fooot - thanks, that was, what I was going for.

This guy got his Turbo arrow up to FL200

Make as many modifications as necessary to make it look like a Mooney M20K/252 which is certified to 28,000'  https://en.wikipedia.org/wiki/Mooney_M20 :)

The Turbo Dakota (PA-28-201T) is very close to what you seem to be describing and is likely much less expensive to buy outright vs. the time and materials required to modify a lowly PA-28-1xx.  The published ceiling is FL200 with its TSIO-360 but at light weights* I'm sure a determined pilot could coax it to FL230 or FL250.
So, the answer is: a big TSIO engine.  The 260hp TSIO-470-B (only TSIO-470 made to my knowledge) would probably do the trick.  A TSIO-520 has taken me to FL250 in a T210 so I know it would probably take a Cherokee at least that high assuming that you successfully attach the engine to the plane (approvals, engineering, mechanical, W&B, etc).
*The Dakota is one of the few small single engine planes with a gross weight of more than twice its empty weight leaving plenty of wiggle room for a pilot seeking to extract better than book performance from the plane.
**Answer assumes you have an O2 system that will do the job at FL250.

One of the biggest drivers is here would be the supplemental oxygen system aboard the aircraft.  Currently a PA 28 is not certified for high-altitude operations i.e. flight above FL260,  though existing turbo normalizing STC kits would physically allow the aircraft to fly higher.   Treading into the death zone requires pressure breathing oxygen systems to live.  There are also additional requirements for avionics and systems needed for high altitude flight eg DMEs, altimeters rated for operation near or in the tropopause, etc.  A Piper Archer was just never intended to tread that high


text:
What exactly was the American WW2 smokebomb used in naval warfare?
In WW2 the Americans used a kind of smoke/gas-bomb that they mounted under the SBD planes in naval warfare.
What was the purpose of that device and what is it called?

The ocean is featureless, floating smoke bombs were used to mark a spot on a body of water so pilots could get back to the same spot. Smoke plumes can be seen from a long distance, they also let you gauge wind direction and speed.
Smoke bombs were often used when attacking submarines, if a pilot spotted a periscope or caught a sub on the surface before it dove he could drop a smoke marker on the spot before coming around to drop a depth bomb on it. Smoke bombs were also used to mark people in the water, for instance downed pilots or sailors, so they could be rescued.

Good answer, if you could add the specific devices used (the OP does specify a military and time period), it would be great.

Do you mean Smoke Floats? Use Google Books search and search for "sbd dauntless smoke float light" will find details.

Page 29 of the Pilot's Flight Operating Instructions, Navy Model SBD-6 Airplanes,
NavAer 01-40SC-I, Sept. 1, 1944, says:

The five float lights (night drift signals) are aft of the flexible gun ammunition box.  These lights are principally used at night to check drift variations, but can also be used during daylight.  The gunner computes the
amount of drift by means of the smoke, or smoky light, which is released when the float strikes the water.


text:
Are there differences between the runway lighting on a land runway and on an aircraft carrier?
How are the lights on aircraft carriers placed and are there differences to the color/position/number of lights at normal airports?

Yes, basically just (dim) Edge and Centerline lights plus the IFLOLS

Welcome to aviation.SE! Others may disagree, but I think this could be half of a good answer :-) If you can add an image of a regular runway, that would make it very easy to compare the two lighting configurations, which I believe is the basic question.


text:
Is there anything in any airport called a "warm apron"?
I heard a pilot said they are located at big airports like LAX. But I couldn't find any information about it.

Was your conversation with the pilot in English? If not, could you add the exact words he used in the original language?

Possible solutions might be airport "hot-spots" (areas of increased risk due to confusing layout), and warm-up or run-up areas on the ramp.

@Pondlife the conversation was in spanish but what JonathanWalters added is correct, I was refering to the warm-up areas near the runway, but I've never heard of that area before.Thank you for your help.

A warm up apron is a portion of the airfield close to the runway entry, where the engine can be warmed up before taking off. It seems to be more frequently used in military documentation.
There are such aprons at Cairns Army Airfield:

Source
Found in FAA regulations, e.g. AC 150/5340-30:

PAPI LHAs must not be located closer than 50 ft from a crossing
  runway, taxiway, or warm-up apron or within the ILS critical area.

But also in other not regulatory documents, here for synonymous of hardstand:

... construction of the RMP test section and warm-up apron (hardstand)
  at the east end of Runway 04-22. The RMP warm-up apron was
  successfully constructed and has been opened for traffic since October
  1992.

Source: Design, Construction and Performance of Resin Modified Pavement at Fort Campbell Army Airfield, Kentucky
A vintage post-card:

Source: eBay

These are sometimes called run-up aprons and its an area where a pilot can perform final preflight checks before taking off as well as engine run-ups and tests where a pilot can do these without worrying about jet blast or propwash kicking up FOD all over a parking apron.  At military bases, this is used as a final once over by ground crews as well as ordies removing the safeties of all external ordnance thus arming the weapons prior to takeoff.


text:
Is it normal to take off with limited flaps on a B737?
Is it safe/normal to take off (fully loaded from Cyprus to Kenya - 6 hours) with very small flaps extended? Model of aircraft: Boeing 737-800. He used whole length of the airfield to take off, the next acceleration took a long time at low level, and the next climb happened very slowly.

That looks like Flaps 1, and that is not only normal and safe, it is very common on relatively long runways (7500' and longer). For slightly shorter runways, a Flaps 5 takeoff is often used, and for the shortest runways (less than 5500', roughly), even Flaps 15 or on some aircraft, Flaps 25.
All of those are entirely safe options.
As the runway gets shorter, you get the best performance -- defined as how much weight you can carry while still meeting all requirements -- with an earlier liftoff. This means, more flaps to enable rotating at a slower speed. The downside of more flaps is more drag, which reduces initial climb performance. To get the most weight possible, you'd use an extremely long runway, a high takeoff speed, and minimal flaps (i.e. Flaps 1 as you had) for the best performance in the climb. But when the runway isn't so long, you start to be more limited in the weight you can carry, and to get the best results, more & more flaps become optimal as the runway gets shorter.
It sounds like your flight was probably pretty heavy -- a full -800 certainly would qualify -- and so the crew took advantage of the long runway to accelerate to a fast takeoff speed using Flaps 1. In the air, the aircraft will fly fine at that weight, but it isn't as nimble and won't accelerate as quickly as a lighter 737 would. If you're used to the performance of a 737 loaded with the fuel for a one or two hour flight, it isn't surprising that the aircraft with enough fuel for a 6 hour flight (plus reserves, in both cases) would seem sluggish in comparison.

It's amazing how much runway the -900ERs can chew up, though. Boeing airport planning docs show that an MTOW takeoff at 30 C/sea level requires 11,000 feet runway length and 40 C/sea level requires 15,000! I remember being a little concerned the first time I took off in one as we blew past the 2,000 ft markers...

@reirab those are temperature extremes of course, and pretty unlikely on Larnaka in winter, in a rainstorm :) Temp at the time the photo was taken was likely 15C or so, 20 at most.

@jwenting There was ~10C

@jwenting I was commenting more just on the variation within the 737s, not on this particular scenario. 30 C isn't really extreme for most parts of the world. The particular takeoff I mentioned would have been at least that, as it was in Tampa. < 30 C there is more uncommon than >= 30 C.

@reirab, the 737-900 is rather heavy for the wings that were designed long ago for significantly smaller aircraft, leading to rather high rotation speed. And with similar acceleration, distance is proportional to square of target speed, so the take-off (and landing) distances get really long.

@JanHudec Indeed, and span extensions aren't really an option due to the need to maintain ADG III. Bigger engines are also difficult, due to the current ones nearly scraping the ground as it is. The -900ER already had to lengthen the landing gear a bit in order to keep the engines off the ground, IIRC.


text:
What rating can I add to a commercial certificate with the least time/effort?
I have an FAA commercial certificate with ASEL, AMEL, ASES, Glider and Instrument ratings (alongside specific type ratings). What additional certificate or rating will require the shortest amount of training to add?
It could be anything from sport pilot through ATP certificate, for any class: weight shift, multi engine seaplane, gyro-copter etc.

now reads "quickest (in terms of prerequisites and\or flight hours)"

Just curious, why are you asking? Why the desire to add something to your license quickly?

Does a Part 107 certificate count? You could get it in a day just by doing the knowledge test but it's a separate certificate, not an add-on to an existing one, so it might not be what you're looking for.

After thinking some more I've voted to close this as unclear because I'm not sure what you consider a valid answer. E.g. you could get Part 107 or Ground Instructor with only written tests, but is that what you mean? Or are you asking about something that gives you more flight privileges? And what about your hours and experience? Is there an 'easy' type rating in an aircraft that you have prior experience in? Do you have enough hours for ATP already? Maybe private balloon (10hrs training) is closest to what you're asking, but I'm really not sure.

Jack Brown's Seaplane Base offers single engine seaplane ratings at private and commercial level.  It takes 2 full days and costs between 1400 USD and 2300 USD depending on your choice of training aircraft.
From their website:

SES Rating
We offer three options of planes for your SES training at the private
  or commercial level, both of which include: 1.5 hours of ground
  instruction, 5 hours of dual instruction, the check ride and the
  examiner’s fee.
Training in the Piper J3-Cub on floats,  1,400.00.
Training in the Maule M-7 on floats,     2,300.00.
Training in the Super Cub on floats,     1,850.00.
If additional flight instruction hours are required they are billable
  at the hourly rate of the aircraft (listed below).

They are located in Winter Haven, FL.